During a drilling operation, data may be transmitted from a downhole transmitter located on a downhole tool included as part of the bottom hole assembly (BHA) of a drill string positioned in a wellbore. The data transmitted from the downhole transmitter may be received by a surface receiver, or by a downhole receiver located elsewhere in the BHA or in an adjacent wellbore. Data transmitted from the downhole transmitter may include, for instance, properties of the surrounding formation, downhole conditions, status of downhole equipment, and the properties of downhole fluids. Electronics present in the BHA may be used for telemetry of data to the surface, collecting data using sensors such as vibration sensors, magnetometers, inclinometers, accelerometers, nuclear particle detectors, electromagnetic detectors, acoustic detectors, acquiring images, measuring fluid flow, determining direction, emitting signals, particles or fields for detection by other devices, interfacing to other downhole equipment, and sampling downhole fluids; The BHA may also include mud motors and steerable drilling systems, such as a rotary steerable system (RSS), which may be used to steer the wellbore as it is drilled. By receiving data from the BHA, an operator may have access to the data collected by the sensors.
The drill string can extend thousands of feet below the surface. Typically, the bottom end of the drill string includes a drill bit for drilling the wellbore. Drilling fluid, such as drilling “mud”, may be pumped through the drill string. The drilling fluid typically cools and lubricates the drill bit and may carry cuttings back to the surface. Drilling fluid may also be used for control of bottom hole pressure.
Examples of telemetry techniques for transmitting data to the surface include mud pulse (MP), electromagnetic (EM), hardwired drill pipe, fiber optic cable, and drill collar acoustic.